Leads having electrodes implanted in or about the heart have been used to reverse life-threatening arrhythmia or to stimulate contraction of the heart. Electrical energy is applied to the heart via an electrode to return the heart to normal rhythm. Leads are usually positioned on or in the ventricle or the atrium and the lead terminals are attached to a pacemaker or defibrillator which is implanted subcutaneously.
One issue concerning, for example, pacemaker leads is the increase in stimulation threshold, both acute and chronic, caused by the interaction between the electrode and body tissue at the point of implant. Approaches to reducing the threshold include the incorporation of drug collars or plugs containing a therapeutic agent such as, for example, dexamethasone or beclomethasone into the lead body. However, the size of the plug or collar required to deliver a therapeutically effective amount of the therapeutic agent prevents a substantial reduction in the overall lead body diameter. Moreover, these devices many not adequately address many of the physiological processes involved in the healing response upon lead implantation.
Another issue concerning pacemaker leads is the difficulty in designing a lead body with fluoropacity for visualization during and after implantation of the lead in a patient's body. Current technology places a radiopaque ring on the lead body for visualization of the lead in viva Radiopaque rings are not amenable to irregular lead body shapes and, again, the size of the radiopaque ring may prevent a substantial reduction in the overall lead body diameter.